Late Summer Rainfall Research Articles

An assessment of Schinopsis brasiliensis Engler (Anacardiacea) for dendroclimatological applications in the tropical Cerrado and Chaco forests, Bolivia

Given the scarcity of instrumental climatic data in the South American tropics, it is valuable to explore the dendrochronological potential of the numerous tree species growing in the region. In this paper, we assessed for the first time the dendrochronological characteristics of Schinopsis brasiliensis, an arboreal species from the dry-tropical Cerrado and Chaco forests in Bolivia and adjacent countries. Similar to most woody species in the Cerrado and Chaco regions, growth rings of S. brasiliensis are delimited by the presence of thin but continuous lines of marginal parenchyma. Based on 22 samples from 15 trees, we present the first ring-width chronology for this species covering the period 1812–2011 (200 years). Additionally, a 106-year floating chronology from S. brasiliensis was developed using cores from four columns from the church of San Miguel, Santa Cruz, built in the period 1720–1740. Standard dendrochronological statistics indicate an important common signal in the radial growth of S. brasiliensis. The comparison of variations in regional climate and ring widths shows that tree growth is directly related to spring-summer rainfall and inversely related to temperature. Following the winter dry season, rainfall in late spring and early summer increases soil water supply, which activates tree growth. In contrast, above-average temperatures during the same period increase evapotranspiration, intensify the water deficit and reduce radial growth. The dependence of S. brasiliensis growth on water supply is evidence of its dendrochronological potential for reconstructing past precipitation variations in the extensive tropical Cerrado and Chaco forest formations in South America. Using wood from historical buildings opens the possibility of extending the chronologies of S. brasiliensis over the past 400–500 years.

Assessment of a lumped coupled flow‐isotope model in data scarce Boreal catchments

AbstractQuantifying streamflow sources within remote, data scarce, Boreal catchments remains a significant challenge because of limited accessibility and complex, flat topography. The coupled use of hydrometric and isotopic data has previously been shown to facilitate quantification of streamflow sources, but application has generally been limited to small basins and short time scales. A lumped flow‐isotope model was used to estimate contributing streamflow sources (soil, ground, and wetland water) over a four‐year period in two large nested headwater catchments (Sapochi and Odei Rivers) in northern Manitoba, Canada. On average, the primary streamflow source was estimated as soil water (60%) in the Sapochi River, and groundwater (54%) in the Odei River. A strong seasonal influence was observed: soil water was the primary streamflow source in summer, changing to groundwater and wetlands during the winter. Interannual variability in streamflow sources was strongly linked to the presence or absence of late summer rainfall. The greatest uncertainties in source quantification were identified during the spring freshets and high precipitation events, and hence, simulations may be improved through explicit representation of the soil freeze/thaw process and data collection during this period. Assessment of primary streamflow components and qualitative uncertainty estimation using coupled isotope‐flow modelling is an effective method for first‐order identification of streamflow sources in data sparse remote headwaters. Copyright © 2016 John Wiley & Sons, Ltd.

Enhancement of Arctic storm activity in relation to permafrost degradation in eastern Siberia

In the last decade, increases in both soil temperature and active layer thickness have been observed in the central Lena River basin, an area located in the centre of continuous permafrost in the Eurasian continent. Increased soil temperatures have been accompanied by corresponding increases in soil moisture within the active layer at many sites throughout the region. These underground hydro-thermal changes are believed to be primarily due to perennially wet climate conditions, rather than the atmospheric warming alone that has resulted in abnormally large amounts of winter snow accumulation and late summer rainfall in the Lena River basin. This study aimed to clarify the linkage between atmospheric and land surface variations in regions of continuous permafrost in eastern Siberia based on in situ observation and atmospheric climatic data analyses. These wet conditions in 2004–2008 were likely caused by the enhancement of cyclones over the Arctic Ocean and eastward propagation of storm activity during late summer and early winter. Water vapour flux was enhanced in conjunction with the manifestation of precipitation in eastern Siberia. As a result, consecutive positive anomalies of winter snow accumulation and precipitation during the subsequent summers effectively humidified land surfaces in the permafrost region from 2005 onwards, which resulted in abrupt soil warming and wetting of both the active layer and the upper part of the permafrost. The positive effects on increasing soil temperatures of both snowfall in winter and rainfall in summer have been observed in eastern Siberia since the 1990s, and have also been demonstrated through land surface simulation. Results of these hydro-climatic changes indicated that the near-surface permafrost in eastern Siberia is vulnerable to the climatic conditions that have arisen due to the acceleration of the hydrological cycle that has resulted from the aforementioned period of warming.

Real-time PCR quantification and spatio-temporal distribution of airborne inoculum of Puccinia triticina in Belgium

In order to better understand the epidemiology of Puccinia triticina and the relationship between airborne inoculum and disease severity, a method for quantifying airborne inoculum was developed using volumetric Burkard 7-day spore traps and real-time PCR. The method was applied using a spore trap network from 1 March to 30 June over a 5-year period. At one site, the inoculum was quantified continuously over 3 years, during which it showed a seasonal distribution, with the highest quantities and detection frequencies occurring between May and June. High mean daily quantities (65.8–121.2 spores/day) and detection frequencies (±20 % of days) were also reported after harvest from September to December. In the coldest months of the year, almost no detection was recorded (1–6 % of days). The study results indicate that the absence of inoculum in the air when upper leaves are emerging could be a limiting factor for the risk of epidemics. Mean daily quantities of airborne inoculum (0–131.4 spores/day) were measured from the beginning of stem elongation (GS30) to the flag leaf stage (GS39). These values were well correlated with the disease severity levels measured during grain development. A multiple regression analysis showed that total rainfall in late summer and autumn and mean minimum temperature in winter positively influence spore density between GS30 and GS39 in the following spring (R2 = 0.73). This relationship and the patterns of airborne inoculum observed in fields strongly suggest the existence of a ‘green bridge’ phenomenon in Belgium. Our study also showed that the quantification of airborne inoculum or its estimation using a weather-based predictive model could be useful for interpreting disease severity models and avoiding over-estimates of disease risk.

Changes in Nutrient Characteristics of Switchgrass for Bioenergy

Switchgrass (Panicum virgatum L.) was identified as a “model” bioenergy crop by the USDOE in 1991. Since then, there has been little research to understand changes in switchgrass quality during the growing season or the effect that drought may have on these quality characteristics. This study determined changes in total N, P, K, S, Ca, Mg, moisture concentration, and dry weight yield through intensive sampling during the growing season. Subsamples from a one‐cut system were harvested on 13 different dates in 2011 and eight different dates in 2012 between late May and early November. Low rainfall in late spring and early summer 2012 created drought conditions that led to some differences between years. In general, the measured variables decreased with time, but dry weight yield increased in both years and peaked around late August. In 2011, a significant rise in N between late July and mid‐August may have been caused by reproductive growth and/or organic matter mineralization, although this has not been documented elsewhere. Differences between normal (2011) and drought (2012) conditions included lower biomass production, reduced N concentrations, increased S and P concentrations in late August, and increased plant moisture in late August and October under drought conditions. Years with drought conditions may allow more staggered harvesting because nutrient ranges are smaller. This will allow a more continuous supply of feedstock to the biorefinery. These data and future economic analyses will allow better decision‐making opportunities for producers.

Unexpected consequences of a drier world: evidence that delay in late summer rains biases the population sex ratio of an insect.

The complexity of animal life histories makes it difficult to predict the consequences of climate change on their populations. In this paper, we show, for the first time, that longer summer drought episodes, such as those predicted for the dry Mediterranean region under climate change, may bias insect population sex ratio. Many Mediterranean organisms, like the weevil Curculio elephas, become active again after summer drought. This insect depends on late summer rainfall to soften the soil and allow adult emergence from their underground refuges. We found that, as in many protandric species, more C. elephas females emerged later in the season. Male emergence timing was on average earlier and also more dependent on the beginning of late summer rainfall. When these rains were delayed, the observed weevil sex ratio was biased towards females. So far, the effects of global warming on animal sex ratios has been reported for temperature-dependent sex determination in reptiles. Our results show that rainfall timing can also bias the sex ratio in an insect, and highlight the need for keeping a phenological perspective to predict the consequences of climate change. We must consider not just the magnitude of the predicted changes in temperature and rainfall but also the effects of their timing.

Long-term decline in grassland productivity driven by increasing dryness.

Increasing aridity and drought severity forecast for many land areas could reduce the land carbon (C) sink. However, with limited long-term direct measures, it is difficult to distinguish direct drying effects from counter effects of CO2 enrichment and nitrogen (N) deposition. Here, we document a >50% decline in production of a native C3 grassland over four decades and assign the forcing and timing to increasing aridity and specifically to declining late-summer rainfall. Analysis of C and N stable isotopes in biomass suggests that enhanced water use efficiency via CO2 enrichment may have slightly ameliorated the productivity decline but that changes in N had no effects. Identical declines in a long-term snow-addition experiment definitively identified increasing late-summer dryness as the cause. Our results demonstrate lasting consequences of recent climate change on grassland production and underscore the importance of understanding past climate–ecosystem coupling to predicting future responses to changing climate.

Antecedent controls on rainfall runoff response and sediment transport in a high arctic catchment

In the High Arctic, late summer rainfall events have the potential to increase discharge and transport substantial amounts of sediment. Past studies have not considered the role of antecedent soil moisture with respect to rainfall‐runoff response, particularly in the context of changing climate. We investigate these processes through multiple major rainfall events and the associated discharge and suspended sediment response, measured in a small watershed at ape ounty, elville sland, unavut. Fluvial and sedimentological responses to two major rainfall events on 9 ul. and 23 ul., 2012, totaling 35.4 and 10.6 mm, respectively, resulted in negligible responses in discharge and suspended sediment mobilization. The magnitude and intensity of these events were not unusual in this region, but the lack of response was substantial when compared with past events of similar magnitudes. The two‐week antecedent period leading up to the 9 ul. rainfall was characterized by exceptional temperatures and high solar radiation, decreasing soil moisture and increasing infiltration potential, all of which substantially diminished the runoff and resultant suspended sediment transport. These results demonstrate that antecedent catchment conditions may substantially attenuate suspended sediment transport responses to multiple major rainfall events and decrease runoff ratios and characterization of these conditions is necessary to accurately model catchment response.

A Method to Linearly Evaluate Rainfall Frequency–Intensity Distribution

AbstractThis study presents a method to linearly evaluate the rainfall frequency–intensity distribution, which is an important component of climatological rainfall characteristics. To grasp and represent the key information of the rainfall frequency distribution by intensity, a two-parameter double exponential function is formulated and fitted to the hourly rainfall observation at each station. The values of the two parameters are estimated by transforming the distribution to a linear pattern. The two parameters determine the location and shape of the fitted distribution curve, and they have different modulating effects in different intensity categories, one governing the low-intensity section and the other dominating the intense rainfall. Through analysis of the estimated parameters, essential features of rainfall distribution can be obtained and assessed. The proposed method is applied to analyze the climatology and long-term variation of the late-summer rainfall in China. It is found that topography and monsoon circulation are two major factors controlling the rainfall frequency–intensity distribution. At stations with high surface altitudes and complex orography, the frequency of light rain is extremely high and the number of intense rainfall events is relatively small. In the plain areas of eastern China, especially those influenced by the main monsoon rain belt, heavy rainfall is more frequent. By tracking the displacement of the parameter pairs, the decadal changes in rainfall frequency–intensity distribution can be clearly visualized and evaluated on a plane constructed by the two parameters. The southern flooding and northern drought pattern can be attributed to the changes in light and moderate rainfall, while the intense rainfall exhibits opposite trends.

Hourly Rainfall Changes in Response to Surface Air Temperature over Eastern Contiguous China

Abstract In this study, late-summer rainfall over eastern contiguous China is classified according to hourly intensity and the changes of moderate, intense, and extreme precipitation in response to variation of surface air temperature are analyzed. The e-folding decay intensity (Imi) derived from the exponential distribution of rainfall amount is defined as the threshold that partitions rainfall into moderate and intense rainfall, and the double e-folding decay intensity (Ie) is used as the threshold to pick out extreme cases. The mean values of Imi and Ie are about 12 and 24 mm h−1, respectively. Between the two periods, 1966–85 and 1986–2005, the ratio between moderate and intense rainfall has experienced significant changes. And the spatial pattern of changes in the percentage of moderate rainfall presents a direct relation with that of the surface air temperature. Based on temperature changes, three regimes, regime N (north China), regime C (central eastern China), and regime S (southeastern coastal area of China), are defined. In warming regimes (regimes N and S), the percentage of moderate rainfall exhibits a decreasing trend. In regime C, where the temperature has fallen, the percentage of moderate rainfall increased prominently. In all three regimes there are significant negative (positive) correlations between the percentage of moderate (intense) rainfall and the temperature. The relation between the extreme rainfall and the surface air temperature is far more regionally dependent. With plenty of water supply and little change in relative humidity, the extreme rainfall increased in regime S. Although regime N also shows strong warming trends, there is no significant trend in extreme precipitation due to the lack of water vapor transportation.

Hydrochemical and sedimentary responses of paired High Arctic watersheds to unusual climate and permafrost disturbance, Cape Bounty, Melville Island, Canada

AbstractHigh Arctic river responses to changing hydroclimatic and landscape processes are poorly understood. In non‐glacierized basins, snowmelt and rainfall generate river discharge, which provides first order control over fluxes. Further factors include the seasonality of precipitation, seasonal active layer development, and permafrost disturbance. These controls were evaluated in terms of sedimentary and biogeochemical fluxes from paired catchments at Cape Bounty, Melville Island, Nunavut during 2006–2009. Results indicate that the source of runoff can be more important than the amount of runoff for sediment, solutes, and organic yields. Although the snowmelt period is typically the most important time for these yields, heavy late summer precipitation events can create disproportionately large yields. Rainfall increases yields because it hydrologically connects areas otherwise isolated. Inorganic solute yields from late summer rainfall are higher because the thick active layer maximizes hydrologic interactions with mineral soils and generates high solute concentrations. Results also indicate that while the catchments are broadly similar, subtle topographic differences result in important inter‐catchment differences in runoff and suspended and dissolved loads. The East watershed, which had less extensive permafrost disturbance, consistently had higher concentrations of dissolved solids. These higher dissolved fluxes cannot therefore be explained by thermokarst features, but rather by deeper active layer development, due to a greater proportion of south‐facing slopes. Although warm temperatures in 2007 led to extensive active layer disturbance in the West watershed, because the disturbances were largely hydrologically disconnected, the total disturbed area was small, and inter‐annual variability in discharge was high, there was no detectable response in dissolved loads to disturbances. Sediment availability increased after 2007, but yields have largely returned to pre‐disturbance levels. Results indicate that seasonality and frequency‐magnitude characteristics of projected increases in precipitation must be considered along with active layer changes to predict the fluvial sedimentary and biogeochemical response to regional climate change. Copyright © 2011 John Wiley & Sons, Ltd.

El Niño–Southern Oscillation–related principal interannual variability modes of early and late summer rainfall over East Asia in sea surface temperature-driven atmospheric general circulation model simulations

[1] A large portion of interannual variability during early summer (May–June mean; hereinafter referred to as MJ) and late summer (July–August mean; hereinafter referred to as JA) rainfall over East Asia is dominated by El Niño–Southern Oscillation (ENSO) events. Four ENSO-related modes have been identified by using empirical orthogonal function (EOF) decomposition analysis on East Asian rainfall for the period 1980–1999, with EOF2 for MJ rainfall (hereinafter referred to as MJ-2; similar notations are used for other modes) corresponding to the developing phase of La Niña events, while MJ-3, JA-1, and JA-2 correspond to the decaying phase of El Niño events. The authors investigate the predictability of ENSO-related MJ and JA rainfall modes by analyzing the outputs of 12 atmospheric general circulation models (AGCMs) of the Atmospheric Model Intercomparison Project Phase II (AMIP II), which were run in an AGCM stand-alone mode and were forced by the monthly historical sea surface temperature (SST) from 1980 to 1999. The results show that although the climatological differences between MJ and JA rainfall are reasonably reproduced by most AGCMs, the four ENSO-related interannual variability modes of MJ and JA rainfall show different predictabilities. While both atmospheric circulation and precipitation anomalies associated with MJ-3 (the slow El Niño decaying mode) are reasonably reproduced by nearly all the models, the JA-1 (MJ-2) mode is only partly reproduced by about two thirds (half) of the AMIP II models. All models fail to reproduce the JA-2 mode. The relatively low skills in predicting both JA-1 and JA-2 modes are primarily due to the bias of the AMIP models in simulating both the intensity and the position of the western North Pacific anticyclone. The predictability of the JA-1 mode is slightly higher than that of JA-2, and the difference results from the stronger and longer persistence of SST anomaly (SSTA) forcing associated with the decaying ENSO events. The low skill of the MJ-2 prediction is due to the weak SSTA forcing associated with the developing phase of La Niña. The skills of the AMIP II models in predicting the leading interannual variability modes of East Asian summer rainfall do not depend on the horizontal resolutions of the models.

Synergistic effects of past historical logging and drought on the decline of Pyrenean silver fir forests

The causal factors and effects of forest declines are not well understood in temperate conifer forests. Most studies have focused on climatic and environmental stressors and have obviated the potential role of historical forest management as a predisposing factor of decline. Here, we assess if the recent silver fir ( Abies alba) decline observed in the Spanish Pyrenees was predisposed by historical logging and incited by warming-induced drought stress. We analysed a dataset of environmental, structural, and historical variables at the tree and stand level including 32 sites with contrasting degrees of defoliation distributed over 5600 km 2. We followed a dendroecological approach to reconstruct historical logging and to infer the effects of warming-induced drought stress on growth. The silver fir decline was more severe and widespread in western low-elevation mixed forests dominated by trees of small size and slow growth. These sites were subject to higher water deficits than eastern sites, where late-summer rainfall as the key climatic variable controlling silver fir growth was higher. Declining sites showed more frequent growth releases induced by historical logging than non-declining sites. Historical logging and warming-induced drought acted as long-term predisposing and short-term inciting factors of silver fir decline in the Pyrenees, respectively. We suggest that biomass increases caused by past intense logging affected the vulnerability of silver fir against late-summer water deficit. Future research in declining temperate conifer forests should consider the interacting role of predisposing historical management and inducing climatic stressors such as droughts.

Complex seasonal cycle of ecohydrology in the Southwest United States

This study investigates the causes for, and distribution of, unimodal versus bimodal seasonal cycle of vegetation greenness in the Southwest United States using extensive site observations, climate data, satellite data, and the Lund‐Potsdam‐Jena (LPJ) vegetation model. Peak vegetation greenness is achieved in a clockwise manner across the Southwest, beginning in spring in the Sonoran Desert following winter rains, then in Utah‐Colorado with snowmelt/summer rains, and finally in New Mexico–eastern Arizona with late summer monsoon rains. At high elevations, spring‐summer snowmelt is critical for supplying the necessary soil moisture to trigger vegetation growth. A bimodal seasonal cycle of vegetation greenness is evident in satellite data and LPJ simulations across eastern Arizona and western New Mexico, characterized by peaks during late spring–early summer and late summer–early autumn. This bimodal green‐up remains a pressing paradox for which many competing hypotheses exist. The mechanism for this seasonal pattern is demonstrated using LPJ and observational data and is found to deviate from the traditional pulse‐reserve paradigm. This paradigm states that rainfall events in arid lands produce nearly immediate pulses of vegetation growth and accumulation of reserves but does not consider cold dormancy, time‐lagged vegetation responses, or rainfall seasonality. The following soil moisture based mechanism for bimodal greening is proposed. The initial peak in vegetation greenness during late spring–early summer results from a break in cold dormancy and benefits from the gradual winter‐long accumulation of deep soil moisture from weak synoptic rain events and snowmelt in colder regions. Limited precipitation and ongoing transpiration, from the initial vegetation greening, trigger a midsummer drying of the soil and a consequential minimum in vegetation activity. Later, pulses of monsoon rainfall in late summer–early autumn support the secondary greening, although significant runoff of brief, intense rainstorms and substantial soil evaporation limit moisture to the upper soil layers.

Indian Summer Monsoon variations could have affected the early-Holocene woodland expansion in the Near East

Postglacial expansion of deciduous oak woodlands of the Zagros—Anti-Taurus Mountains, a major biome of the Near East, was delayed until the middle Holocene at ~6300 cal. yr BP. The current hypotheses explain this delay as a consequence of a regional aridity during the early Holocene, slow migration rates of forest trees, and/or a long history of land use and agro-pastoralism in this region. In the present paper, support is given to a hypothesis that suggests different precipitation seasonalities during the early Holocene compared with the late Holocene. The oak species of the Zagros—Anti-Taurus Mts, particularly Quercus brantii Lindl., are strongly dependent on spring precipitation for regeneration and are sensitive to a long dry season. Detailed analysis of modern atmospheric circulation patterns in SW Asia during the late spring suggests that the Indian Summer Monsoon (ISM) intensification can modify the amount of late spring and/or early summer rainfall in western/northwestern Iran and eastern Anatolia, which could in turn have controlled the development of the Zagros—Anti-Taurus deciduous oak woodlands. During the early Holocene, the northwestward shift of the Inter-Tropical Convergence Zone (ITCZ) could have displaced the subtropical anticyclonic belt or associated high pressure ridges to the northwest. The latter could, in turn, have prevented the southeastward penetration of low pressure systems originating from the North Atlantic and Black Sea regions. Such atmospheric configuration could have reduced or eliminated the spring precipitation creating a typical Mediterranean continental climate characterized by winter-dominated precipitation. This scenario highlights the complexity of biome response to climate system interactions in transitional climatic and biogeographical regions.

Drought-triggered false ring formation in a Mediterranean shrub

Recently, the Mediterranean region has experienced unprecedented drought. Climate models continue to predict an increase in drought frequency and duration, which increases the importance of quantifying the response of already drought-tolerant Mediterranean plants to increased drought. We examined the wood anatomy and dendroecological features of a Mediterranean shrub, Arbutus unedo L., at a xeric and a mesic site on the Italian island of Elba to identify shrub growth response to drought. Cross-sectional microsections of A. unedo stems were stained, described, and crossdated. Annual ring widths of radial microsections were measured and compared with regional climatic variables. False rings (intra-annual bands of latewood typically formed in response to a specific stressor) were visible in the wood samples when viewing radial microsections under high magnification. False ring formation coincided with below-average rainfall in late summer at the xeric site, and below-average rainfall and high temperatures in spring and summer at the mesic site. If increased drought occurs in the Mediterranean region, it is likely that plants in this region will experience a drought-induced growth response similar to that seen in A. unedo, and slight differences in drought tolerance may become more important as plants compete for moisture under drier conditions.

Heavy daily-rainfall characteristics over the Gauteng Province

Daily rainfall over the Gauteng Province, South Africa, was analysed for the summer months of October to March using 32-yr (1977 to 2009) daily rainfall data from about 70 South African Weather Service stations. The monthly and seasonal variation of heavy rainfall occurrences was also analysed. Three 24-h heavy rainfall classes are defined considering the area-average rainfall. A significant rainfall event is defined when the average rainfall exceeds 10 mm, a heavy rainfall event when the average rainfall exceeds 15 mm and a very heavy rainfall event when the average rainfall exceeds 25 mm. January months have the highest monthly average rainfall as well as the highest number of heavy and very heavy rainfall days. The month with the second-highest number of heavy and very heavy rainfall days is February followed by March and October. December has the second-highest monthly average rainfall and the most days with rain. However, it is also the month with the lowest number of heavy and very heavy rainfall days. The highest 24-h rainfall recorded at a single station during the 32-yr period was 300 mm in December 2006. However, rainfall exceeding 115 mm at a single rainfall station in the Gauteng Province is very rare and does not occur every year. January months receive these events more than any other month but this only transpires in approximately a third of years. The central and north-western parts of the Province experience the most events where the rainfall at a single station surpasses 75 and 115 mm. With regard to seasonal rainfall, the 1995/96 summer rainfall season had the highest seasonal rainfall during this 32-yr period followed by the 1999/2000 season. The 1995/96 season had above normal rainfall in both early and late summer but the 1999/2000 season was dry in early summer and very wet in late summer. Significantly high seasonal rainfall is associated with above-normal rainfall in late summer.

WRF/ARPEGE-CLIMAT simulated climate trends over West Africa

The Weather Regional Forecast (WRF) model is used in this study to downscale low-resolution data over West Africa. First, the performance of the regional model is estimated through contemporary period experiments (1981–1990) forced by ARPEGE-CLIMAT GCM output (ARPEGE) and ERA-40 re-analyses. Key features of the West African monsoon circulation are reasonably well represented. WRF atmospheric dynamics and summer rainfall compare better to observations than ARPEGE forcing data. WRF simulated moisture transport over West Africa is also consistent in both structure and variability with re-analyses, emphasizing the substantial role played by the West African Monsoon (WAM) and African Easterly Jet (AEJ) flows. The statistical significance of potential climate changes for the A2 scenario between 2032 and 2041 is enhanced in the downscaling from ARPEGE by the regional experiments, with substantial rainfall increases over the Guinea Gulf and eastern Sahel. Future scenario WRF simulations are characterized by higher temperatures over the eastern Tropical Atlantic suggesting more evaporation available locally. This leads to increased moisture advection towards eastern regions of the Guinea Gulf where rainfall is enhanced through a strengthened WAM flow, supporting surface moisture convergence over West Africa. Warmer conditions over both the Mediterranean region and northeastern Sahel could also participate in enhancing moisture transport within the AEJ. The strengthening of the thermal gradient between the Sahara and Guinean regions, particularly pronounced north of 10°N, would support an intensification of the AEJ northwards, given the dependance of the jet to the position/intensity of the meridional gradient. In turn, mid-tropospheric moisture divergence tends to be favored within the AEJ region supporting southwards deflection of moist air and contributing to deep moist convection over the Sahel where late summer rainfall regimes are sustained in the context of the A2 scenario regional projections. In conclusion, WRF proved to be a valuable and efficient tool to help downscaling GCM projections over West Africa, and thus assessing issues such as water resources vulnerability locally.

Environmental Correlates of Breeding in the Crested Caracara (Caracara cheriway)

ABSTRACT. We evaluated the influence of weather on reproduction of the Crested Caracara (Caracara cheriway) in an agricultural landscape in south-central Florida. We used a mixed logistic-regression modeling approach within an information-theoretic framework to examine the influence of total rainfall, rainfall frequency, and temperature on the number of breeding pairs, timing of breeding, nest success, and productivity of Crested Caracaras during 1994–2000. The best models indicated an influence of rainfall frequency and laying period on reproduction. More individuals nested and more pairs nested earlier during years with more frequent rainfall in late summer and early fall. Pairs that nested later in each breeding season had smaller clutches, lower nest success and productivity, and higher probability of nest failure. More frequent rainfall during early spring months that are usually characterized by water deficit (March–May), more frequent rainfall during the fall drawdown period (September–November), a...

Patterns of diversity, endemism and distribution of bees (Insecta: Hymenoptera: Anthophila) in southern Africa

For southern Africa, patterns of bee diversity and endemism were studied with a special focus on South Africa and the Cape Floral Kingdom. Based on distribution records of 645 species incorporated in the “Southern African Bee Database” (SouthABees), the pattern of bee diversity was analysed on a 2° × 2° grid. The resulting map shows a bicentric pattern, with highest species diversity located in the arid west and in the relatively moist east. The investigation of distribution patterns of 516 South African species identified twelve distribution types that largely coincide with patterns in the seasonality of precipitation: winter rainfall, early to mid summer rainfall, late to very late summer rainfall and rain all year. The largest number of bee species is associated with the winter rainfall area (46.3% of the fauna) and with the early to mid summer rainfall area (36.5% of the fauna). Consequently South Africa is a centre of bee diversity of global significance. The most important centres of endemism are the winter rainfall area in the west (27.3% of total fauna endemic) and the early to mid summer rainfall area (29.1% of total fauna endemic) in the east. The relationship between bee/plant diversity patterns and speciation is discussed.